FIELD OF THE INVENTION
The present invention relates to a vertical type pressure casting method used for accurately casting aluminum alloy products, comprising the steps of closing gates communicating with the cavities of clamped molds with a counter-tip, pouring melt into the portion of the interior of a sleeve which is between the counter-tip and a lifted plunger tip, displacing the counter-tip to open the gates and allow the melt to flow into the cavities by the force of gravity, and thereafter pressure-filling the cavities with the melt using the plunger tip. More particularly, the present invention concerns a vertical type pressure casting method comprising the steps of first lowering a plunger tip, subsequently displacing a counter-tip before the plunger tip reaches the melt in the sleeve to open the gates to the cavities and allow the melt to flow into the cavities by the force of gravity, and thereafter pressurizing the melt to fill the cavities, the melt being thus injected into the cavities smoothly and continuously at a low rate to prevent gas from being sucked therein, the cross-sectional area of the gates being set so that the ratio of the volume of the products to the cross-sectional area of the gates is 20-40 (volume of products (cm.sup.3)/ cross-sectional area of gates (cm.sup.2)=20-40), the speed of the plunger tip and the length of time between commencing the downward movement of the plunger tip and opening the gates being set to an optimum level determined in relation to the temperatures of the molds and melt, a percentage of the melt to be fed into the cavities by the force of gravity at the time when the plunger tip reaches the melt in the sleeve being set to 30-70, if the plunger tip does not move the percentage of the melt which is to flow into the cavities by the force of gravity alone being set to not less than 30%, the speed of the melt through the gates when pressure filling the cavities with the plunger tip being set to 0.4-0.8 m/sec.